One problem with roller shades is vertical tracking, i.e., making the shade roll up accurately on the roller. This problem is not particularly serious with stretchable shade material such as PVC. Thus, despite the use of telescoping rollers having different outside diameters, PVC shades will track well without difficulty. This is not the case, however, with essentially non-stretchable sheet material such as impregnated cloth or filament reinforced plastic. With such materials, if the tracking starts off line by even a slight amount, the shade will roll up off line, cause harmful binding on one side margin, and present an unsightly, tipped bottom margin. The most common cause of faulty tracking is variation in the outside diameter of the shade-supporting roller and since there are advantageous of ease of adjustment in using telescoping rollers, the artisans have been interested for many years in providing telescoping shade rollers with ways to compensate for the differences of diameter, so that the shade will track accurately. For example, an early patent to Rice (U.S. Pat. No. 1,898,686) provided the smaller roller section with an enlarged end for this purpose. Gossling in one case (U.S. Pat. No. 3,203,468) provided a cylindrical fiber tube around the smaller roller section to make up for the difference in diameter, and Miller (U.S. Pat. No. 4,102,385) provided an extra length of shade material to wrap around the smaller roller section small enough to make up for the diameter difference.
There have been problems, however, with these prior approaches. For example, with Gossling, the portion of the fiber tube which is cut off must be slid off the end of the smaller roller. This means that the smaller roller cannot be provided with an enlarged flanged head. This is a disadvantage because the inner roller can be pushed too far in if it has no enlarged flanged head on it. The problem with the Miller approach is that, when lock-seam tubes are used, the smaller roller will necessarily have a groove on its surface and the material of the final several wraps of the shade will depress into the groove such that the trimming knife cannot reach it. This is a nuisance because it requires hand severing. It is, in fact, why Miller discloses using shade material which can be torn along pre-scored lines. Neither shade material of impregnated cloth, nor of filament reinforced plastic can be suitably pre-scored, but yet, such material is far more attractive than the pre-scored vinyl, and it can be accurately trimmed.
It is, therefore, a primary object of the present invention to provide a semi-adjustable shade and roller combination for essentially non-stretchable shade material, in which the shade may be mechanically trimmed conveniently accurately to width without cutting, and with which the finally trimmed and adjusted shade will vertically track perfectly. Another object is to provide such a shade and roller combination with an enlarged flanged head on the end of the inner roller to facilitate adjustment of the roller to the trimmed shade without the risk of being pushed in too far.